NAME: PID: Group Name: BioSci 110, Fall 08 Exam 3

Transcription

1 For questions 1 and 2 use the phylogeny to the right. 1. With what group of species do rodents share the most traits? a. amphibians b. dinosaurs and birds c. *primates d. ray-finned fish e. sharks 2. Which node represents the most recent common ancestor of amphibians and primates? a. B b. *C c. D d. E e. F 3. In the tree below, assume that the ancestor had a long tail, ear flaps, external testes, and fixed claws. Based on the tree and assuming that all evolutionary changes in these traits are shown, what traits do bears have? Note: Traits shown on the tree should be matched to the nearest red line. a. long tail, ear flaps, external testes, and fixed claws b. short tail, no ear flaps, external testes, and fixed claws c. short tail, no ear flaps, abdominal testes, and fixed claws d. *short tail, ear flaps, external testes, and fixed claws e. long tail, ear flaps, abdominal testes, and retractable claws 4. Speciation has occurred when two or more subpopulations: a. Become geographically separated from one another b. *Achieve reproductive isolation c. Experience genetic divergence d. Compete for limiting resources 1

2 5. Hurricane Katrina had a devastating effect on New Orleansʼ historic population of Live Oaks, many of which were well over 100 years old. Oaks in low-lying areas were particularly devastated - many died as a result of having their roots submerged in the floodwaters for weeks. Oaks occurring on higher ground were more likely to survive because they did not experience long-term flooding. The change in allele frequencies that occurred in New Orleansʼ Live Oaks is an example of: a. *Genetic drift b. Gene flow c. Artificial selection d. Natural selection e. Sexual selection 6. Carl Woeseʼs work in the 1970ʼs and 80ʼs used RNA sequences to construct phylogenetic trees for different groups of organisms. His results indicated: a. Relationships cannot be determined by molecular methods b. Whittakerʼs 5-kingdom classification is an accurate representation of evolutionary relatedness c. *Prokaryotes are more diverse than initially thought d. Heterotrophs are not related to autotrophs 7. Cows have bacteria that live in their digestive tract that help them digest cellulose from grasses. The bacteria allow the cows to extract more nutrients and calories from grass than they would if they didnʼt have these bacteria. The bacteria live their entire life cycle within the gut of the cow and do not survive outside of the cow gut. The relationship between the cow and its gut bacteria is an example of a: a. commensalism b. competition c. * mutualism d. parasitism e. predation 2

3 In the 1970ʼs, evolutionary biologist, John Endler began studying wild populations of guppies in Venezuela. He was impressed by the range of variation he observed among guppies living in different pools within the same stream. Endler carefully measured size, color, and placement of spots on guppies and started to observe a strong correlation between where guppies lived in a particular stream and whether male fish were bright or drab. Female guppies are all drab, regardless of location. Data from 3 pools within the same stream are indicated in the table below. Pool Number guppies Average Male Coloration Average Female Coloration Number of Predators Bright, multi-colored, large spots Medium color, medium spots Drab colors, small spots near tail drab, small spots Pike cichlids: 0 Blue acara: 0 Rivulus: 12 drab, small spots Pike cichlids: 0 Blue acara: 7 Rivulus: 15 drab, small spots Pike cichlids: 17 Blue acara: 20 Rivulus: 5 Pool 2 Pool 1 Pool 3 3

4 1. (2 pts) Describe 2 potential consequences that variation in male coloration might have on fitness in guppies. - bright colors could attract more females - drab color may benefit guppies by allowing them to escape predation (camouflage) 2. (1 pt) In describing the relationship between male coloration and fitness, [male coloration / fitness] is the dependent variable. Fitness 3. (5 pts) Construct a graph that shows your prediction about the relationship between male coloration and fitness for each of the 3 pools. You may construct this as 3 separate graphs or as 3 plots within the same graph. In either case, label axes and indicate which plot is associated with Pool 1, Pool 2, and Pool 3. Fitness Pool 1 Pool 2 Pool 3 Male coloration (drab bright) 4. (9 pts) For each of the 3 pools, indicate whether you think selection is or is not acting on the population, what the likely selective agent is, and the basis for your claim. Do you think selection is acting on this population? If yes, what is the likely selective agent? Pool 1 yes female choice Pool 2 yes female choice AND predators Describe your rationale for determining whether selection is or is not a factor for this population. There are more bright than dull males. Predator pressure is lowest in this pool, so bright colors are not a significant risk. Females are all dull indicating the variation in the males is due to female choice (sexual selection). Because predator pressure is low, males gain a mating advantage if they are bright. intermediate color is most abundant in this population due to opposing selective pressures both acting on the guppies (sexual selection and predation) Pool 3 yes predators predators are most abundant in this pool, so bright color is risky. Males that are camouflaged (drab) have the highest fitness. 5. (3 pts) An undergraduate research assistant conducts a project in which she moves 50 guppies from Pool 1 into Pool 3 and observes the fish over several months. Predict the outcome of her experiment and explain your rationale. It is likely that survival (thus, fitness) will be low for the transported guppies. Pool 1 guppies are mostly bright this is the least favored phenotype in Pool 3 due to the abundance of predators. Bright-colored males will be most attractive to females, but are at a high risk for predation. 4

5 6. (10 pts) A complete explanation of natural selection would include 5 fundamental principles of evolution indicated in the left column of the table below. In the right column, explain (in a sentence or less) how each concept is represented in (or relevant to) the case of guppy coloration in Venezuelan streams. Genetic Variation Origin of Variation Inheritance Fitness Population Change Individual guppies in the population differ from one another in coloration and spot patterns. Genetic differences (e.g., different alleles) account for the phenotypic variation we see in the color and spot patterns of the guppies. (+2) +1 = phenotypic differences are observed +1 = phenotype differences are linked to genotype differences Random mutations in existing alleles result in different sequences of bases, thus new alleles. Random mutations resulted in alleles for brighter coloration and spots in the guppies. (+2) Genetic information is passed from parent to offspring through the gametes. New alleles that conferred brighter colors were passed on to offspring of the guppies. (+2) +1 = genetic information is passed from parent to offspring through gametes +1 = more fit alleles are passed on to offspring Guppies differ in their ability to reproduce, and this difference is based on their phenotypes and is influenced by the environment. (+2) Alleles for bright colored guppies conferred the greatest fitness advantage, and therefore guppies displaying these phenotypes will survive and reproduce, passing on their genes to their offspring. Over time, the alleles for bright color will become more abundant in the population (because bright colored guppies are reproducing the most) and the population will change to become brighter, on average. (+2) +1 = Guppies with a higher fitness reproduce more +1 = Overtime, the frequency of alleles changes to reflect these different rates of reproduction 7. (12 pts) In a box-and-arrow model, concepts are structures that are linked by behaviors. Behaviors are short phrases or linking words that clearly and concisely describe the relationship between structures. Behaviors are generally active, and therefore tend to be verbs, while structures are concepts or nouns. a. (10 pts) In the space below, construct a box and arrow model that demonstrates your understanding of the following concepts in the context of this problem about guppy coloration: gene, allele, DNA molecule, chromosome, protein, phenotype, mutation, genetic variation, fitness, and selection. Use language in the structures and behaviors of your model that are specific to this case. For example, instead of using gene as a structure in your model, use gene for indicating the specific type of gene relevant to the guppy case. Each concept listed above is represented accurately in association with a correct behavior. 2 pts awarded for correctly representing the associations indicated below, with correct/accurate descriptive words: (1) chromosome-dna: DNA is represented as being equivalent to or a component of a chromosome; hierarchical organization is represented correctly (2) gene-mutation-allele-variation: alleles are indicated as alternative versions of genes; new alleles arise as the result of mutations in existing genes. The consequence of mutations in existing alleles is that new alleles arise. Mutation is the origin of all variation and the ultimate source of genetic variation in a population (3) protein-phenotype: alternative alleles code for the production of different proteins that are expressed as different phenotypes. Individuals in a population differ in their phenotypes owing to the activity of proteins encoded by different alleles. (4) variation selection fitness: selection acts on variation in the population; as a result, certain phenotypes have increased or decreased fitness (5) model was specific to the guppy problem b. (2 pts) In a sentence or less, what is the function of your model? 5

6 NAME: PID: Group Name: BioSci 110, Fall 08 Exam 3 The model should illustrate both: a) how genetic and phenotypic variation arises in a population, and b) how environment acts on that variation resulting in differential fitness for different phenotypes (i.e., evolution by natural selection). Variable must be consistent with information represented in model and must go beyond the function of origin of variation because selection and fitness have been added to this model. Anticipated functions include: evolution of the guppy population. 8. (8 pts) In Endlerʼs data, 3 species of fish (pike cichlids, blue acara, and rivulus) were listed as predators of guppies. Pike Cichlid Blue Acara Rivulus Guppy a. (4 pts) Describe 2 adaptations that help (or could help) the predators above become more successful in preying on guppies. Explain how the adaptations you list are adaptive. Lots of answers: bigger and sharper teeth, faster (more hydrodynamic), bigger eyes, etc. 1 pt each for naming a trait; 1 pt for explaining HOW it is adaptive b. (4 pts) Describe 2 adaptations that help (or could help) guppies become more successful in avoiding predation. Explain how the adaptations you list are adaptive. Lots of answers: faster (more hydrodynamic), dull coloration (camouflage), toxins, etc. 1 pt each for naming a trait; 1 pt for explaining HOW it is adaptive 9. (8 pts) Consider the interactions between two of the predatory fish, blue acara and pike cichlids. a. (1 pt) What type of ecological interaction characterizes the relationship between blue acara and pike cichlids? a. commensalism b. *competition c. mutualism d. parasitism e. predation b. (2 pts) In a sentence or less, explain your answer. As predators, they overlap in their use of a limiting resource (they both feed on a limited number of guppies) that is the definition of competition. c. (3 pts) BRIEFLY describe (or draw) a simple experiment you could perform to confirm the type of interaction you predicted for the blue acara and rivulus. - this question was not counted in the scoring You could: a) supplement the limiting resource add more guppies than either population could possibly consume, or b) isolate the populations of acara and rivulus d. (2 pts) Describe the results from your experiment that would confirm your prediction about the type of interaction between blue acara and pike cichlids. If competition were a factor between acara and rivulus (or cichlids), then fitness of each should go up following either experiment. This would support the prediction of competition b/c when populations compete, fitness for both is reduced through the competitive interaction. 6

7 10. (14 pts) For questions a f, you must show your work to receive full credit, including all equations and calculations! This problem was completed through a clicker series in class on 11/25. In guppies, fan-shaped tails result from the expression of a recessive allele, f. In one of Endlerʼs pools, 64 of the 100 guppies had a fan-shaped tail. a. (1 pt) What is the Hardy-Weinberg predicted frequency of the f allele (q) in this population of guppies? Here, we start by assuming that the population is in HWE. If so, then the frequency of 64/100 (.64) represents the frequency of the homozygous, recessive genotype, ff. This is represented in HWE as q 2 ; therefore, q 2 =.64. To solve for q, take the square root. q =.8 b. (1 pt) What is the Hardy-Weinberg predicted frequency of the F allele (p) in this population of guppies? P = 1 q = =.2 c. (4 pts) Calculate the Hardy Weinberg predicted frequencies for all possible genotypes. PREDICTED genotype frequencies are generated from the HWE equation: p 2 + 2pq + q 2 = 1 FF: HWE predicted value is p 2 = (.8) 2 =.64 Ff: HWE predicted value is 2pq = 2(.8)(.2) =.32 ff: HWE predicted value is q 2 = (.2) 2 =.04 d. (4 pts) Researchers observed that there were no heterozygotes in this population of guppies. Calculate the observed genotype frequencies for this population. FF: =.36 Ff: 0 ff: 64/100 =.64 e. (2 pts) Without actually calculating Chi-Square, do you expect that this population is or is not in Hardy- Weinberg equilibrium? Explain. If the values for predicted and observed genotype frequencies are similar, then the population IS in HWE. If the values for predicted and observed genotype frequencies are different, then the population IS NOT in HWE. f. (2 pts) Assume that your conclusion in e is verified statistically. What is the biological interpretation of this outcome? (i.e., what does this mean?) If you said they are similar, this indicates the population is NOT evolving If you said they are different, this indicated the population is evolving 7